1. Field of the Invention
The present invention relates to a glass bulb for a cathode ray tube having a two-dimensional matrix code comprised of a plurality of dots in a predetermined portion of an outer side surface of the glass bulb, a method for producing such glass bulb and a method for producing a cathode ray tube using such glass bulb.
2. Discussion of the Background
There has been known a technique that information on the glass bulb or information on operating conditions (including information on the particulars of operations) is directly written as marked characters or a code in an outer side surface of a glass bulb for a cathode ray tube (hereinbelow, referred to as a glass bulb), and manufacturing steps for the glass bulb are controlled based on the information read. Generally, the writing of such information in the outer side surface of the glass bulb is conducted by directly printing a heat-resistant material or attaching a heat-resistant label, or marking by sand-blasting or laser.
For example, JP-A-2-87442 proposes a method for controlling manufacturing procedure wherein a bar code is marked by using a CO.sub.2 gas laser masking method and the bar code is read whereby a mistake in combining parts of a cathode ray tube, which may take place in manufacturing, can be prevented. Further, such a technique that the particulars of a product manufactured can be obtained from characters marked by laser is also known from JP-U-63-20251.
However, the conventional techniques using printing or laser masking to write the characters or the code had a problem that all required information had to be separately given to individual products. For example, in the laser masking method, since laser beams had to be passed through a mask to write information, it was impossible to change the particulars of information without changing the mask. Accordingly, it was difficult to write information for a relatively short time for a large quantity of glass bulbs conveyed during manufacturing steps.
In the conventional technique, there was a quantitative restriction on information to be written in by means of characters and a bar code. Accordingly, information inherent to the glass bulb such as the kind (size), the transmittance of the glass bulb, application or non-application to an anti-reflection treatment, a manufacture line used and so on and information on operating conditions have been given to a large number of products which were grouped for controlling in mass production. That is, the conventional techniques are inappropriate as an information means to identify a large number of glass bulbs.
Heretofore, conventional characters or a bar code marked by laser on the outer side surface of glass bulbs by a glass bulb manufacturer are insufficient for a cathode ray tube manufacturer to utilize the information written by the glass bulb manufacturer. Accordingly, the cathode ray tube manufacturer has written its own information by means of characters or a bar code so that manufacturing steps can be controlled. That is, glass bulb manufacturers and cathode ray tube manufacturers have not used common characters or a bar code.
There has been known a general technique of using a laser to mark characters or bar codes on glass products. However, there has not been proposed such a technique that characters or the like including a large amount of information which can identify individually glass bulbs are marked on the surface of a glass product such as a glass bulb which is transparent, does not have a flat surface and has a mat-surface-like fine recesses and projections, and the information marked therein can be read by means of a pick-up device.
Further, in the steps of producing panels and funnels in the glass bulb manufacturers, there are a variety of combinations among a processing line, a mold, a forming machine, a hot processing machine and so on. Accordingly, if a trouble or a defective product takes place in a step of producing, it takes much time to trace the cause, and on the other hand, an appropriate way of resolution has not been proposed.
Further, there is a problem in manufacturing steps for the glass bulb such that, for example, it is difficult to supply products manufactured by the same mold or the same machine in a forming or hot processing step, in the intentionally optimum combination, to the next polishing step at which there are a large number of lines for polishing. This difficulty is applicable also to cathode ray tube manufacturers.
In short, due to restrictions to an amount of information to be written in and difficulty in writing the characters and so on for glass bulbs, there is a limit in using the characters or codes in manufacturing steps in each of the glass bulb manufacturers and cathode ray tube manufacturers. Thus, there has not been known a method for producing a glass bulb or a cathode ray tube wherein marked characters or codes can be used commonly for both manufacturers, to make it unnecessary for the cathode ray tube manufacturer to use its own characters or codes.
On the other hand, there has recently been an increased spread of using bar codes and needs for coding a greater amount of information and putting information in a smaller space. In response to this, a two-dimensional matrix code has been known. The two-dimensional matrix code is a code system wherein information is written in both directions of longitudinal and lateral, i.e., two-dimensional directions. However, the application of the two-dimensional matrix code, in particular, a two-dimensional matrix code comprised of a plurality of dots, to a glass bulb has not been studied. Further, a technique of identifying glass bulbs by using the two-dimensional matrix code comprised of a plurality of dots, and a technique of controlling manufacturing steps for glass bulbs or cathode ray tubes based on the information of the two-dimensional matrix code marked in the glass bulbs, have not been known.